Nickel inhibition of calcium precipitation by ureolytic mixed microorganisms under batch conditions

The respirometric assessment of the inhibitory impact of Ni(II) on substrate utilization and microbial carbonate precipitation (MCP) by ureolytic mixed microorganisms was investigated with a glucose containing mineral medium under batch conditions over an incubation period of 134 h. The IC25 was determined as 224 mg Ni(II) L−1 from the BOD values of samples. The interpretation of kinetic data showed that the substrate removal rate fitted a zero-order at the beginning of the incubation period and first-order during the last period, for a range of Ni(II) concentrations between 0 and 512 mg L−1. Increasing Ni(II) concentrations from 0 to 512 mg L−1 reduced the substrate degradation rate constant from 10.8 to 5.3 mg L−1 h−1 for zero-order rate constant (k0), and from 0.015 to 0.002 h−1 for first-order rate constant (k1). The zero- and first-order reaction rates during incubation period were equalized to the reaction rate of the Monod equation in order to determine the kinetic constants, half saturation concentration (KS) and maximum substrate removal rate (Rmax). BOD removal rate was inhibited accordingly to mixed inhibition model with increasing Ni(II) concentrations during the calcification process. Also, the inhibition of calcium precipitation was observed at a higher Ni(II) concentration because of inhibition of ammonium production in these samples.